If history is any guide, once La Nina becomes well-established in the tropical Pacific Ocean, global temperatures should drop noticeably relative-to-normal.
Earlier this year, there were signs that a weak El Nino in the tropical Pacific Ocean could continue through the fall and even into the upcoming winter season, but there is now substantial agreement amongst numerous computer forecast models that La Nina conditions are likely to become established over the next couple of months and current observations back this notion. La Nina is a naturally occurring oceanic cycle that produces colder-than-normal sea surface temperatures (SSTs) in the equatorial Pacific Ocean whereas El Nino is associated with warmer-than-normal SSTs. The formation of La Nina in the tropical Pacific Ocean will likely have important ramifications around the world including significant impacts on the upcoming winter season, next summer’s tropical season, and global temperatures.
Compilation of statistical and dynamical computer forecast models of ENSO in coming months. Most of these models predict La Nina conditions will form over the next couple of months in the tropical Pacific Ocean.; courtesy IRI/CPCComputer model forecasts support the formation of La Nina
Numerous independently-made computer forecast models depict a change from the current near-neutral conditions in the tropical Pacific Ocean to La Nina conditions by the winter of 2017-2018. The plume of model El Nino Southern Oscillation (ENSO) model forecasts from mid-September indicate a transition to La Nina conditions are quite likely to take hold by later this fall. Indeed, some models are predicting a fairly strong La Nina by the middle of the upcoming winter season with sea surface temperatures as much as 1.5°C below-normal in the “Nino 3.4” region (central tropical Pacific).
Sea surface temperatures have indeed changed dramatically in the tropical Pacific Ocean between the spring and today with a “wavy” pattern of colder-than-normal water (bottom panel, blue region) now showing up in the same area that exhibited widespread warmer-than-normal SSTs back in April 2017 (top panel, yellow/orange region).
Impact on global temperatures
Global temperatures spiked across the world during the last strong El Nino event which reached a peak during the latter part of 2015 and early part of 2016 and they have trended slightly lower this year from that high point. According to Weather Bell Analytics, NOAA’s CFSv2 global temperature anomalies spiked in 2016 to +0.457°C above the 1981-2010 average and those anomalies – while still above normal – have dropped slightly this year to +0.382°C (through October 2nd). If history is any guide, once La Nina becomes well-established in the tropical Pacific Ocean, global temperatures should drop noticeably relative-to-normal.